# Homework Help: Chem help pleaseeee : How many Fe atoms and how many moles of Fe atoms are in 400.0 g

1. Jul 16, 2011

1. The problem statement, all variables and given/known data

How many Fe atoms and how many moles of Fe atoms are in 400.0 g of iron?

3. The attempt at a solution

Ok. i attempted to find the number of moles by using 400/55.8 to get 7.17 but that is wrong?! please tell me ehy this is wrong. i set up a proportion like this 55.8g Fe = 1 mol
all over 400.0 grams =x and i solved for that x. i know its wrong, but why?

2. Jul 17, 2011

### pmsrw3

Re: chem help pleaseeee : How many Fe atoms and how many moles of Fe atoms are in 400

Beats me. I would have said that's exactly what you're supposed to do. How do you know it's wrong? Were you given a different number as the solution?

By the way, the phrasing "How many moles of Fe atoms..." is peculiar. Normally one just asks "How many moles of Fe..." If you answer is wrong, then perhaps it is because your prof is making some unusual subtle distinction by including the word "atoms" in the second part of the question.

3. Jul 17, 2011

### Ygggdrasil

Re: chem help pleaseeee : How many Fe atoms and how many moles of Fe atoms are in 400

Perhaps your answer is not being counted as correct because 400.0g has four significant digits, and your answer should have four significant figures as well.

4. Jul 17, 2011

Re: chem help pleaseeee : How many Fe atoms and how many moles of Fe atoms are in 400

well i know its wrong because my online hw is marking it wrong. im really confused because i even tried changing the number to 4 sigfigs instead of 3 but it was wrong again. What am i doing wrong?!

5. Jul 17, 2011

### pmsrw3

Re: chem help pleaseeee : How many Fe atoms and how many moles of Fe atoms are in 400

Maybe you should try a more accurate number for the atomic weight of iron. Also, what about the number of atoms question?

6. Jul 17, 2011

Re: chem help pleaseeee : How many Fe atoms and how many moles of Fe atoms are in 400

you are right! thank you. i used a more specific number and i got the correct answer. and i just multuplied by avagadros number for atoms. thanks for all your help, everyone.

7. Jul 17, 2011